Fluid-compressing apparatus



Augfl 1, 1925.,

- R. N. EHRHART FLUID COMPRESSING APPARATUS Original Filed Dec. 7, 1921 III/IIIIIIIIIIII COMPRESSED.

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lfetented f ing.

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RAYMOND N. EI-IRHART, OF EDGEWOOD, IENNSYLVANIA, ASSIGNOR T0 ELLIOTT GOM- PANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

FLUID-COMFRESSING APPARATUS.

Application filed December 7, 1921, Serial To all whom it may concern:

Be it known that I, RAYMOND N. EHR- HART, acitizen of the United States, residing at Edgewood, Allegheny County, Pennsylvania, have invented a. new and useful Improvement in Fluid-Compressing Apparatus, of which the following is a full, clear, and exact description.

The present invention relates broadly to fluid compressing apparatus, and more particularly to ejectors adapted for use with condenser and similar installations where it is desired to maintain certain pressure conditions below atmospheric or effect the removal of air or otherfluids.

It has heretofore been proposed to construct single stage ejectors having long and short nozzle structures so arranged that the short nozzles effect preliminary compression of fluids entrained by their operation and deliver the entrained and entraining fluids directly to long noz- .zle structures without any loss of efficiency such as produced by first converting the velocity energy established by the short nozzle structure into pressure energy, and then reconverting into velocity energy by the long nozzle structure. Such constructions, although possessing many advantageous features, have not been proportioneo whereby a highly etficient compressing action has been secured throughout a long range and at higher pressures.

The present invention, while embodying ertain of the features of such prior constructions, relates primarily to the relative proportioning of the respective parts whereby high efiiciency is obtained when compressing great amounts of air from low pressures, and higher efficiency, than has heretofore been obtained, is obtained when compressing great amounts of air from higher pressures, such, for example, as from 2 to 5 inches of mercury.

The foregoing and other objects of the present invention, together with their attendant advantages, will be apparent as the invention becomes better understood by reference to the accompanying specification No. 520,530. Renewed December 19, 1924.

and drawings forming a part thereof, it being premised that changes may be made in the details of construction and manner of operation without departing from the spirit of my invention or the scope of my broader claims.

Figure 1 is a longitudinal sectional view, partly broken away, through an ejector constructed in accordance with the present invention;

Figure 2 is a tranverse sectional view on the line II- H of Figure 1, looking in the direction of the arrows;

Figure 3 is a transverse sectional view on the line III-J11 of Figure 1, looking in the direction of the arrows, and

Figure at is a graphic illustration of the operation of an ejector embodying the present invention.

Referring more particularly to Figures 1 to 3 of the drawings, there is illustrated an ejector comprising a diiiuser structure having a converging portion 2 and a diverging portion 3 connected by a throat portion 4:.

he open end of the converging portion 2 of the diffuser communicates with a connection 5 through which the fluid to be compressed or entrained enters the ejector.

Carried by the ejector structure is a steam chamber 6 having a suitable opening for the admission of the steam to be used as the compressing or entraining medium. Connected with the steam chamber 6 is a plurality of short accelerating nozzles 7 which may project slightly into the converging portion of the diffuser, if desired, butwhich preferably terminate outside of the diffuser, as shown. Also connected with the steam chamber is a plurality of long propelling nozzles 8 which project well into the converging portion of the diffuser. Both the long and short nozzles are divergent, making them suitable for expanding steam at a relatively great pressure to the low pressure existing in the suction chamber of the ejector.

As before pointed out, the section of the diffuser having the smallestdiameter is termed the throat. The cross-sectional area diffuser.

at this point is termed the throat area. The portion of the convergent end of the diffuser atthe end of the long nozzles 8, and lying slightly beyond the section line III-III of Figure 1, is the mouth of the The mouth area designates the area of the diffuser at this point after the cross-sectional area of the long nozzles is deducted therefrom. This mouth area is the passage through which the steam is delivered from the short nozzles 7 to the long nozzles 8, and is substantially as indicated by the shaded portion in Figure 3.

The present. ejector is so proportioned that the throat area of the diffuser is greater than the outlet area of the long nozzles, but is less than the mouth area. This necessarily means that the mouth area must be greater than the outlet area of the long nozzles.

Calculations which have been computed for the construction of expanding nozzles call for a ratio of divergence which is greater than that which I have found to produce the best results. For example, the short nozzles which expand steam from the steam line pressure, which may be M0 pounds per square inch absolute, to apressure of 1 inch of mercury, should theoretically'have'a ratio of divergence of substantially 32. In other words, the outlet area of these nozzlesshould be substantially 32 times their throat area. My experiments have shown, however, that better results are obtained when theoutlet .areais approximately 10 times that of the throat area, but that good results are obtained when the ratio of'divergence varies from 8 to 32. In any case, however, for efiicient results, I find that the ratio of divergence should be materially less than that theoretically required when expanding fronr the initial steam pressure to the pressure at the .termination of the nozzles. However, irrespective of the departure of the present nozzles from the theoreticalcalculation, I find that both sets of nozzles should have a ratio of divergence which is within 30% of each other.

When nozzles are operated with a diverg ence ratio less than that called for by calculation incident to initial steam pressure and discharge pressure, such nozzles are spoken of as being under-expanded. I find that for the best results, the long nozzles should be less under-expanded than the short nozzles, preferably, however, within 30% of. each other as set forth.

lVith steam pressures for the {propelling nozzles varying from 100 to 140 pounds per square inch absolute, the long nozzles should pass more steam than the shortnozzles, preferably more than two times as much, but considerably less than three times as much. The higher the steam pressure, the greater is the amount of steam required through the shorter nozzles in relation to the longer nozzles. For a pressure of approximately HO pounds per square inch absolute of the propelling steam, the long nozzles should pass about 2.66 times as much steam 'as the short nozzles. For a 200 pound pressure the long nozzles should pass approximately twice as much steam as the short nozzles.

For efficient results, it will be understood that the total mouth area with a construction such as herein disclosed, may be divided into five theoretical divisions, which Imay term interstlce areas, which interstice areas take care of the flow of en-trained and entraining fluid from the short or accelerating nozzles. These interstice' areas are designed and proportioned with respect to the volume of flow through the corresponding accelerating nozzles. which deliver thereto, so as to adequately take care of said flow, and are also proportioned with respect one to the other in such manner that no interstice area is less than fifty per cent (50%) nor more than one hundred and fifty per cent (150%) of the average interstice area, when all of the accelerating nozzles deliver the same amount of steam. This ensures the steam from all of the accelerating nozzles reaching the compressing nozzles at substantially the same velocity. This velocity for efficient operation should be greaterthan 7 50 feet'per second and less than 2000 feet per second, approximately 1500 feet per second being very effective.

In an ejector of this type, I find that the shorter nozzles effect a material compression of the entrained fluid, so that when exhausting from a range of from 1 to 5 inches of mercury they effect a compression of the fluid before it is delivered for entrainment to the "larger nozzles of from 3 to 10 inches of mercury. In general, the ratio of com pression accomplished by the first nozzles is less than 4, said ratio becoming less as the amount of fluid entrained or compressed, increases. Forgood performance it is necessary tofhave a ratio of compression of at least 2 for the short set of nozzles. For example, if the ratio of compression for the short set of nozzles is three when exhausting from a pressure of 1 inch of mercury, fluid would be delivered to the long nozzles at a pressure of 3 inches of mercury. With a construction such as above set forth, there is provided an ejector producing results substantially as illustrated graphically in Figure at bythe curve AA. In this fig ure, the vertical scale shows the absolute pressure, in inches of mercury, obtained in the suction chamber of the ejector when compressing the entrained fluid, such asair, to a pressure slightly above that of the atmosphere. The horizontal scale shows the amount of air compressed by approximately 650 pounds of moving steam at approximately 140 pounds absolute pressure. In this figure there is also shown a comparison curve B-B which illustrates the results .obtained as the throat area of the long nozzles increases with respect to that of the short nozzles, and as the outlet area of the long nozzles more nearly approaches or be comes greater than the throat area, and the mouth area decreases with respect to the long nozzle outlet area or with respect to the diffuser throat area. WVith such changes it will be apparent that the efficiency of the ejector is very slightly increased at low pressures, but materially decreased at higher pressures such as from 2 to 5 inches of mercury. With this comparison curve, it becomes apparent that the proportioning herein set forth is of considerable importance as it provides an ejector having a materially greater operating range with much greater efficiency than existing ejectors, at higher pressures, and substantially the same efficiency, as existing ejectors, at lower pressures.

It is understood that by long and short nozzles as used throughout the specification and claims, I mean, respectively, those nozzles terminating nearer and farther from the throat of the diffuser.

I claim:

I. In a single stage ejector, diffuser struc ture, long nozzle structure projecting well into said diffuser structure, and short nozzle structure, the area of the diffuser structure at its throat being greater than the outlet area of the long nozzle structure, substantially as described.

2. In a single stage ejector, diffuser structure, long nozzle structure projecting well into said diffuser structure, and short nozzle structure, the outlet area of the long noz zle structure being less than the area of said diffuser at its throat and less than the mouth area of the diffuser, substantially as described.

3. In a single stage ejector, diffuser structure, long and short diverging nozzle structure, said long nozzle structure projecting well into the diffuser, the outlet area of the long nozzle structure being greater than the outlet area of the short nozzle structure and less than the area of said diffuser at its throat, substantially as described.

4. In a single stage ejector, diffuser structure, long nozzle structure projecting well into said diffuser structure and forming a mouth, and short nozzle structure, the area of the diffuser at its throat being less than the area of said mouth, substantially as described.

5. In a single stage ejector, a diffuser, long and short nozzle structure, said long nozzle structure projecting well into said diffuser and forming a mouth, the mouth area being greater than the outletarea of the long nozzle structure, substantially as described.

6. In a single stage ejector, a diffuser structure, diverging long and short nozzle structure, said long nozzle structure'projecting well into said diffuser structure, the ratio of divergence of said nozzle structures being within 80% of one another, substantially as described.

7. In a single stage ejector, a diffuser structure, long and short diverging nozzle structure, the long nozzle structure projecting well into said diffuser structure, and both of said nozzle structures being proportioned so that the ratio of divergence is within a range of from 8 to 32, substantially as described.

8. In a single stage ejector, a diffuser structure, long and short diverging nozzle structure, the long nozzle structure projecting well into said diffuser structure, and both of said nozzle structures being proportioned so that the ratio of divergence is less than 32, substantially as described.

9. In a single stage ejector, a diffuser structure, under expanded long and short diverging nozzle structure, the long nozzle structure projecting well into said diffuser structure, and both of said nozzle structures being proportioned so that the ratio of divergence is greater than 8, substantially as described.

10. In a single stage ejector, a diffuser structure, long and short nozzle structure, all of said nozzle structures being underexpanded, substantially as described.

11. In a single stage ejector, diffuser structure, long nozzle structure, and short nozzle structure, said long nozzle structure projecting well into the diffuser, both of said nozzle structures being under-expanded with the short nozzle structure under-en panded to a greater extent than the long nozzle structure, substantially as described.

12. In a single stage ejector, diffuser structure, long nozzle structure, and short nozzle structure, said long nozzle structure projecting well into the diffuser, both of said nozzle structure being under-expanded with the short nozzle structure under-expanded to a greater extent than the long nozzle structure, the ratios of divergence of said nozzle structures being within 30% of one another, substantially as described.

13. In a single stage ejector, diffuser structure, long and short nozzle structure, said long nozzle structure projecting well into said diffuser structure and passing more than 2 but less than 3 times as much propelling fluid as said short nozzle structure, substantially as described.

14. In a single stage ejector, a diffuser structure, long nozzle structure projecting well into said diffuser, short nozzle structure cooperating therewith for delivering fluid to the long nozzle structure at a V8- locity of from 750 to 2000 feet per second, both of said nozzle structures being underexpanded and having divergence ratios Within 30% of one another, the long nozzle structure forming a mouth having an area greater than the outletarea of the dong nozzle structure and Jgneater than the thmoat area of .said diffuser, substantially as dc- 1 scribed. v

In testimony whereof Ihave hereunto set my hand. 7 i a I RAYMOND N. .EHRHART. 

